A process that requires an expenditure of ATP energy to move molecules across a cell membrane. Usually moved against the concentration gradient with the aid of specific carrier (transport) proteins.
A domain of organisms that include prokaryotic microbes that live in harsh anaerobic environments. Probably the most primitive life-forms known.
Centrioles (microtubule-organizing centers)
A cellular organelle (composed of microtubles) that organizes the mitotic spindle during mitosis. A pair of centrioles is usually in the center of a microtubule-organizing center in animal cells.
Present in plasma membrane and organelle membranes of eukaryotic cells. Cholesterol molecules embedded in the interior of the membrane and help to make the membrane less permeable to water-soluble substances. Rigid structure of cholesterol molecules helps stabilize the membrane.
Microscopic, hairlike processes on the exposed surfaces of certain eukaryotic cells. Cilia contain a core bundle of microtubules and can perform repeated beating movements. They are also responsible for the swimming of many single-celled organisms.
Relatively long, motile processes that extend from the surface of a cell. Eukaryotic flagella are longer versions of cilia. Flagellar undulations drive a cell through a fluid medium. Like cilia, flagella have 9 + 2 arrangement of microtubles covered by the cell's plasma membrane.
A basic type of tissue that includes bone, cartilage, and various fibrous tissues. Connective tissue supports and binds.
Connective Tissue: Loose/Areolar
Strong, flexible fibers of protein collagen are interwoven with fine, elastic, and reticular fibers, giving loose connective tissue its elastic consistency and making it an excellent binding tissue (e.g. binding the skin to underlying muscle tissue).
Connective Tissue: Fibrous
Collagen fibers are densely packed and may lie parallel to one another, creating very strong cords, such as tendons (which connect muscles to bones or to other muscles) and ligaments (which connect bones to bones).
Connective Tissue: Adipose
Type of loose connective tissue that consists of large cells that store lipid. Most often, cells accumulate in large numbers to form what is commonly called fat.
Connective Tissue: Cartilage
Hard, yet flexible tissue that supports such structures as the outer ear and forms the entire skeleton of such animals as sharks and rays.
Connect Tissue: Bone
Lie within lacunae, but matrix around them is heavily impregnated with calcium phosphate and calcium carbonate, making this kind of tissue hard and ideally suited for its functions of support and protection.
Connective Tissue: Blood
Connective tissue in which fluid called plasma suspends specialized red and white blood cells plus platelets.
The contents of a cell surrounding the nucleus. Consists of a semifluid medium and organelles.
In the cytoplasm of eukaryotic cells, an internal protein framework of microtubules, microfilaments, and intermediate filaments by which organelles and other structures are anchored, organized, and moved about.
A hollow cylinder of tubulin subunits. Involved in cell shape, motion, and growth. Functional unit of cilia and flagella. It is one of three major classes of filaments of the cytoskeleton.
Cytoskeleton: Intermediate Filaments
The chemically heterogenous group of protein fibers, the specific proteins of which vary with cell type. One of the three most prominent types of cytoskeletal filaments. Made of fibrous proteins.
Component of cytoskeleton. Involved in cell shape, motion, and growth. Helical protein filament formed by the polymerization of globular actin molecules.
The random movement of molecules from one location to another because of random thermal molecular motion. Net diffusion always occurs from a region of higher concentration to a region of lower concentration.
Diffusion: Simple Diffusion
The process of molecules spreading out randomly from where they are more concentrated to where they are less concentrated until they are evenly distributed.
Diffusion: Facilitated Diffusion
Diffusion in which a substance is moved across a membrane from a region of higher concentration to a region of lower concentration (down its concentration gradient) by carrier protein molecules.
Net movement of water across a selectively permeable membrane driven by a difference in concentration of solute on either side. The membrane must be permeable to water but not to the solute molecules.
Physiological process by which substances move across a plasma membrane into the cell via membranous vesicles or vacuoles.
Endoplasmic Reticulum: Rough & Smooth
Cytoplasmic organelle composed of a system of interconnected membranous tubules and vesicles. Rough ER has ribosomes attached to the side of the membrane facing cytoplasm, and smooth ER does not. Rough ER functions in protein synthesis, while smooth ER functions in lipid synthesis.
The cellular covering of internal and external surfaces of the body. Consists of cells joined by small amounts of cementing substances. Epithelium is classified into types based on the number of layers deep and the shape of the superficial cells.
Epithelial Tissue: Simple Squamous
Consists of a single layer of tightly packed, flattened cells with a disk-shaped central nucleus. Location: Air sacs of lungs, kidney, lining of heart, blood vessels, and lymphatic vessels. Function: Allows passage of materials by diffusion and filtration.
Epithelial Tissue: Stratified Squamous
Consists of many layers of cells. Location: Lines esophagus, mouth, and vagina. Keratinized variety lines the surface of the skin. Function: Protects underlying tissues in areas subject to abrasion.
Epithelial Tissue: Simple Columnar
Consists of a single layer of elongated cells. Location: Lines digestive tract, gallbladder, and excretory ducts of some glands. Function: Absorption, enzyme secretion.
Epithelial Tissue: Pseudostratified (psuedostratified columnar epithelium)
A tuft of cilia tops each columnar cell, except for goblet cells. Location: Lines the bronchi, uterine tubes, and some regions of the uterus. Function: Propels mucus or reproductive cells by ciliary action.
Epithelial Tissue: Columnar (simple columnar epithelium)
Consists of a single layer of elongated cells. The arrow points to a specialized goblet cell that secretes mucus. Location: Lines digestive tract, gallbladder, and excretory ducts of some glands. Function: Absorption, enzyme secretion.
The domain that includes the true bacteria.
Having a true nucleus. A cell that has membranous organelles, mostly the nucleus. All organisms except bacteria are composed of eukaryotic cells.
The process by which substances move out of a cell. The substances are transported in the cytoplasmic vesicles, the surrounding membrane of which merges with the plasma membrane in such a way that the substances are dumped outside.
Movement of material across a membrane as a result of hydrostatic pressure.
A double layer (bilayer) of proteins and phospholipids, and is fluid rather than solid.
1. Phospholipids have one polar end and one nonpolar end.
2. Cholesterol is present in plasma membrane and organelle.
3. Membrane proteins are individual molecules attached to the inner or outer membrane surface.
The glycoprotein and glycolipid covering (cell coat) that surrounds many eukaryotic cells.
The membrane-bound cytoplasmic organelle where the proteins and lipids made in the endoplasmic reticulum are modified and stored.
The ability of each cell to maintain a constant internal environment.
Proposed endosymbiont theory. Promposed that eukaryotes formed when large, nonnucleated cells engulfed smaller and simpler cells. (An endosymbiont is an organism that can live only inside another organism, forming a relationship that benefits both partners. Symbiosis is an intimate association between two organisms of different species. The merging of these different species to produce evolutionary new forms is called symbiogenesis.)
Cytoplasmic, membrane-bounded organelle that contains digestive and hydrolytic enzymes, which are typically most active at the acid pH found in the lumen of lysosomes.
Individual molecules attached to the inner or outer membrane surface (peripheral proteins) or embedded in it (intrinsic proteins).
Membrane-bound organelle that specializes in aerobic respiration (oxidative phosphorylation) and produces most of the ATP in eukaryotic cells.
The type of tissue that allows movement. The three kinds are skeletal, smooth, and cardiac. Tissue made of bundles of long cells called muscle fibers.
Muscle Tissue: Smooth
Type of muscle tissue in the walls of hollow organs. Visceral muscle.
Muscle Tissue: Cardiac
Specialized type of muscle tissue found only in the heart.
Muscle Tissue: Skeletal
Muscle consisting of cylindrical multinucleate cells with obvious striations; the muscle(s) attached to the animal's skeleton; voluntary muscle.
The type of tissue composed of individual cells called neurons and supporting neuroglial cells.
1. Cell nucleus. A spheroid body within a cell, contained in a double membrane, the nuclear envelope, and containing chromosomes and one or more nucleoli. The genetic control center of a eukaryotic cell.
2. The cell bodies of nerves within the central nervous system.
3. The atom's central core, containing protons and neurons.
Double membrane forming the surface boundary of a eukaryotic nucleus. Consists of outer and inner membranes perforated by nuclear pores.
Allow materials to enter and leave the nucleus, and give nucleus direct contact with endoplasmic reticulum. Size of pores prevents DNA from leaving nucleus, but permits RNA to be moved out.
A small structure within the nucleus of a cell that transcribes ribosomal RNA and assembles ribosomal subunits.
A part of a cell that performs a specific function. A membrane-bound sac or compartment.
A thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and may viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus and other sub-cellular structures.
Outermost membrane of a cell. Its surface has molecular regions that detect changes in external conditions and act as a selective barrier to ions and molecules passing between the cell and its environment. Consists of a phospholipid bilayer in which are embedded molecules of protein and cholesterol. The external covering of protozoan.
A cell that lacks nuclei and other organelles. Eubacteria and Archaea.
Cytoplasmic organelle that consists of protein and RNA, and functions in protein synthesis.
The ability of the plasma membrane to let some substances in and keep others out.
Any small membrane-bound space or cavity formed in the protoplasm of a cell. Functions in either food storage or water expulsion.
A newly discovered organelle that is shaped like an octagonal barrel that may function as a "cellular truck".